Experimental studies of the crystallography of the precipitation of β vanadium hydride

The structure of the interface between β vanadium hydride plates and the parent b.c.c. solid solution of hydrogen in vanadium has been studied by transmission electron microscopy, and measurements have been made of the shape strain and orientation relationship. The results are generally in good agreement with the predictions of the phenomenological theory of martensitic transformations. The prediction that the interface dislocations generating the lattice invariant shear should be resolvable has been confirmed, and direct confirmation obtained of the hypothesis that the complementary shear system is {112} 〈111〉. For the identity correspondence and specific shear system (112)_B [111]_R the predictions of the theory that the habit plane is near (2̄27)_B and the displacement direction near [22̄7]_B have been confirmed by the electron microscopy and the shape strain measurements. The measured magnitudes of both shape and complementary strains agree well with predicted values. Orientation determinations from Laue and Kossel patterns indicate that the [001] direction of the hydride is inclined to the (001) plane and are compatible with monoclinic hydride structures in which either χ or β is greater than 90°. However, measurements of the orientation relationship are generally in better agreement with predictions of the theory for structures with β 〉 90°.